Bottom Line:
The peptide bond model N-methylacetamide self-assembles with a range of dihalotetrafluorobenzenes forming co-crystals that all show the occurrence of orthogonal hydrogen and halogen bonds.

fig2: Partial crystal packing showing how infinite 1D chains (horizontally positioned) formed by NMA via N–H···O HBs further interact with 14DITFB via Br···O XBs in 3c (top) and I···O XBs in 3f (bottom). The disorder on the NMA molecule is omitted for clarity.

Mentions:
Only one of the XB donor sites of the DXTFBs in 3a–e is involved in the XB with the carbonyl oxygen atom. Differently, in 3f, both of the iodine atoms of 14DITFB are halogen-bonded to the carbonyl oxygens of two NMA molecules belonging to two different hydrogen-bonded chains. In all of the six co-crystals, the oxygen atom of NMA is simultaneously involved in short HBs. Special attention during the analysis of the crystal structures has been given to the angle α, which has been defined as the angle between XB and HB, ∠X–O–N as shown in Scheme 1. These angles in 3a–f vary in the range 77.9–98.5°, thus demonstrating the intrinsic tendency of HB and XB to occur orthogonal to each other when sharing the same sp2 O atom (Fig. 2).

fig2: Partial crystal packing showing how infinite 1D chains (horizontally positioned) formed by NMA via N–H···O HBs further interact with 14DITFB via Br···O XBs in 3c (top) and I···O XBs in 3f (bottom). The disorder on the NMA molecule is omitted for clarity.

Mentions:
Only one of the XB donor sites of the DXTFBs in 3a–e is involved in the XB with the carbonyl oxygen atom. Differently, in 3f, both of the iodine atoms of 14DITFB are halogen-bonded to the carbonyl oxygens of two NMA molecules belonging to two different hydrogen-bonded chains. In all of the six co-crystals, the oxygen atom of NMA is simultaneously involved in short HBs. Special attention during the analysis of the crystal structures has been given to the angle α, which has been defined as the angle between XB and HB, ∠X–O–N as shown in Scheme 1. These angles in 3a–f vary in the range 77.9–98.5°, thus demonstrating the intrinsic tendency of HB and XB to occur orthogonal to each other when sharing the same sp2 O atom (Fig. 2).

Bottom Line:
The peptide bond model N-methylacetamide self-assembles with a range of dihalotetrafluorobenzenes forming co-crystals that all show the occurrence of orthogonal hydrogen and halogen bonds.